The demand for downsizing electronic components has accelerated three-dimensional packing by which a plurality of electronic members are stacked to form an electronic member laminated body having a multilayer structure. In addition, further downsizing of electronic components such as an electronic member laminated body has been studied. In such a situation, an electronic member joining layer for joining (bonding) electronic members to each other in an electronic member laminated body, for example, a joining layer for joining a plurality of members to each other constituting a pressure sensor, has become an extremely thin film, and a much finer structure has been formed. Such a three-dimensionally-packed electronic member laminated body is required to include each electronic member with no damage in a (corresponding) joining part and to include electronic members that are stacked parallel to each other.
To address the demands, a method of protecting an underlayer wire in order to obtain a highly reliable electronic member laminated body, a method of interposing a spacer between electronic members in order to stack a plurality of electronic members while maintaining the electronic members parallel to each other, and other methods have been studied. Such a method is exemplified by a method disclosed in Patent Literature 1. In the method, when a plurality of electronic members are stacked, spacers are disposed on a face of an electronic member in a scattered-dot pattern, and then another electronic member is stacked on the face.
However, the spacer disclosed in Patent Literature 1 is formed with a bump that is obtained by applying a paste in a scattered-dot pattern and curing the paste, and thus the spacer is likely to have an uneven diameter. As a result, the clearance between the electronic members is likely to be uneven.
Patent Literature 2 discloses a method of interposing a spacer between electronic members to be joined when a plurality of electronic members are stacked.
However, the spacer disclosed in Patent Literature 2 is a planar member (having a rectangular solid shape or a disk shape) for enlarging the coating area of a synthetic resin and is not a particle spacer for making the clearance between electronic members uniform.
Separately, an adhesive layer including spacer particles has been studied. For example, Patent Literature 3 describes an adhesive that consists essentially of a thermosetting resin composition and rigid plastic fine particles having a particle diameter that substantially defines the film thickness of the adhesive after curing. Patent Literature 3 also describes, in an example, that an adhesive film that contains rigid plastic fine particles having an average particle diameter of 20 μm and has substantially the same film thickness (21 μm or 22 μm) as the average particle diameter of 20 μm of the rigid plastic fine particles can bond a silicon device with a lead frame.
However, as for the composition and the physical properties of the rigid plastic fine particles, Patent Literature 3 merely describes “for example, fine particles of a vinyl polymer obtained by polymerizing a monomer containing divinylbenzene”, and the physical properties such as compressive strength of the rigid plastic fine particles are quite unknown. The adhesive thus has a high probability of causing a problem due to an excessively high compressive strength of the rigid plastic fine particles or an excessively high compressive strength of the rigid plastic fine particles.
Rigid plastic fine particles having an excessively high compressive strength may scratch a member in contact with the adhesive film due to the excessively rigid plastic fine particles. The adhesive film containing rigid plastic fine particles having an excessively high compressive strength has poor deformability. This deteriorates the performance of a device including the adhesive film when a member in contact with the adhesive film is required to be deformed (for example, when the member in contact with the adhesive film is a diaphragm of a pressure sensor). Rigid plastic fine particles having an excessively low compressive strength have a smaller anti-compression force in a practical application range. When the adhesive film is pressurized, the rigid plastic fine particles are broken or largely deformed, and the adhesive film fails to maintain an appropriate film thickness. In order to impart an appropriate strength to the adhesive film containing rigid plastic fine particles having an excessively low compressive strength, the adhesive film is required to contain a larger number of the rigid plastic fine particles. This increases the production cost.
Patent Literatures 4, 5, and 7 disclose an adhesive for an electronic component including spacer particles having an average particle diameter of 2 to 200 μm, a CV value of 10% or less, and a K value of 980 to 10,000 N/mm2. Patent Literatures 6 and 8 disclose an adhesive for an electronic component including spacer particles having a CV value of 10% or less and preferably having an average particle diameter of 3 to 200 μm and a K value of 980 to 4,900 N/mm2. Here, the K value is a numerical value determined in accordance with the formula below.K=(3/√2)·F·S−3/2·R−1/2 
(In the formula, F is the load value (kgf) at 10% compressive deformation of spacer particles, S is a compressive deformation (mm) at 10% compressive deformation of spacer particles, and R is the radius (mm) of spacer particles)
Patent Literatures 4 to 8 describe no measurement temperature for the K value, but Patent Literature 12, of which applicants are the same as those of Patent Literatures 4 to 8, defines the K value at 20° C. The measurement temperature of the K value in Patent Literatures 4 to 8 is thus supposed to be room temperature.
By using the spacer particles described in Patent Literatures 4 to 8 in an adhesive for an electronic component and joining two or more layers of electronic members with the adhesive for an electronic component, the distance between the electronic members can be maintained with high precision, and a highly reliable electronic member laminated material can be obtained.